Use of an ablatometer to measure short-term ablation of exposed ground ice

1985 ◽  
Vol 22 (12) ◽  
pp. 1767-1773 ◽  
Author(s):  
Antoni G. Lewkowicz
Keyword(s):  
Spatial Variability ◽  
Net Radiation ◽  
Short Term ◽  
Ground Ice ◽  
Solar Insolation ◽  
Average Value ◽  
Banks Island ◽  
Energy Inputs ◽  
Continuous Record ◽  
High Degree

An instrument (ablatometer) was developed to measure rates of ablation of exposed ground ice. When the ablatometer is mounted on a melting ice face and linked to a portable micrologger, a continuous record of short-term ablation is obtained.The ablatometer was tested on the headwall of an active ground-ice slump located in southwest Banks Island, Northwest Territories. In general, it performed satisfactorily with little or no instrument-induced melt of the ice. Data for sunny days showed a strong diurnal rhythm of ground-ice ablation and considerable microscale spatial variability. Rates of ablation and their spatial variation were lower on cloudy days, illustrating the importance of solar insolation in inducing melt. Measurements beneath a debris cover following active-layer collapse suggest that ablation soon ceases and does not recommence until after the debris is removed by mud flow.As a result of the high degree of spatial variability in energy inputs and consequently in ablation rates, results from a single ablatometer may not be representative. If two or more instruments are mounted concurrently on exposed ice, an average value of the energy used in ablation can be determined. This value can then be compared with measurements of energy fluxes such as net radiation.

scholarly journals Rate of Short-Term ablation of Exposed Ground Ice, Banks Island, Northwest Territories, Canada

1986 ◽  
Vol 32 (112) ◽  
pp. 511-519 ◽  
Author(s):  
Antoni G. Lewkowicz
Keyword(s):  
Turbulent Energy ◽  
Multiple Regression Equation ◽  
Net Radiation ◽  
Energy Term ◽  
Short Term ◽  
Ground Ice ◽  
Incident Solar Radiation ◽  
Independent Variables ◽  
Banks Island ◽  
South West

AbstractEnergy fluxes and resultant short-term ablation rates were measured at a ground-ice slump on south-west Banks Island. Net radiation, as a proportion of the ablation flux, is greatest on days with high incident solar radiation, whereas on overcast days, sensible- and latent-heat inputs may supply more than half the necessary energy. A multiple regression equation using net radiation and a turbulent-energy term as independent variables explains 79% of the variation in the measured ablation fluxes. Overall, at least 60% of the energy used for ablation at the slump is derived from net radiation.

scholarly journals Rate of Short-Term ablation of Exposed Ground Ice, Banks Island, Northwest Territories, Canada

1986 ◽  
Vol 32 (112) ◽  
pp. 511-519 ◽  
Author(s):  
Antoni G. Lewkowicz
Keyword(s):  
Turbulent Energy ◽  
Multiple Regression Equation ◽  
Net Radiation ◽  
Energy Term ◽  
Short Term ◽  
Ground Ice ◽  
Incident Solar Radiation ◽  
Independent Variables ◽  
Banks Island ◽  
South West

AbstractEnergy fluxes and resultant short-term ablation rates were measured at a ground-ice slump on south-west Banks Island. Net radiation, as a proportion of the ablation flux, is greatest on days with high incident solar radiation, whereas on overcast days, sensible- and latent-heat inputs may supply more than half the necessary energy. A multiple regression equation using net radiation and a turbulent-energy term as independent variables explains 79% of the variation in the measured ablation fluxes. Overall, at least 60% of the energy used for ablation at the slump is derived from net radiation.

Spatial Variability of Contaminant Transport in a Fractured Till, Avedøre Denmark

1999 ◽  
Vol 30 (4-5) ◽  
pp. 333-360 ◽  
Author(s):  
Larry McKay ◽  
Johnny Fredericia ◽  
Melissa Lenczewski ◽  
Jørn Morthorst ◽  
Knud Erik S. Klint
Keyword(s):  
Hydraulic Conductivity ◽  
Spatial Variability ◽  
Field Experiment ◽  
Contaminant Transport ◽  
Tracer Test ◽  
Conductivity Measurements ◽  
Fine Grained ◽  
Downward Migration ◽  
Rapid Transport ◽  
High Degree

A field experiment shows that rapid downward migration of solutes and microorganisms can occur in a fractured till. A solute tracer, chloride, and a bacteriophage tracer, PRD-1, were added to groundwater and allowed to infiltrate downwards over a 4 × 4 m area. Chloride was detected in horizontal filters at 2.0 m depth within 3-40 days of the start of the tracer test, and PRD-1 was detected in the same filters within 0.27 - 27 days. At 2.8 m depth chloride appeared in all the filters, but PRD-1 appeared in only about one-third of the filters. At 4.0 m depth chloride appeared in about one-third of the filters and trace amounts of PRD-1 were detected in only 2 of the 36 filters. Transport rates and peak tracer concentrations decreased with depth, but at each depth there was a high degree of variability. The transport data is generally consistent with expectations based on hydraulic conductivity measurements and on the observed density of fractures and biopores, both of which decrease with depth. Transport of chloride was apparently retarded by diffusion into the fine-grained matrix between fractures, but the rapid transport of PRD-1, with little dispersion, indicates that it was transported mainly through the fractures.

scholarly journals Midwinter melts in the Canadian prairies: energy balance and hydrological effects

2019 ◽  
Vol 23 (4) ◽  
pp. 1867-1883 ◽  
Author(s):  
Igor Pavlovskii ◽  
Masaki Hayashi ◽  
Daniel Itenfisu
Keyword(s):  
Surface Runoff ◽  
Hydrological Cycle ◽  
Remote Sensing Data ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Net Radiation ◽  
Present Climate ◽  
Canadian Prairies ◽  
Energy Inputs ◽  
Hydrological Effects

Abstract. Snowpack accumulation and depletion are important elements of the hydrological cycle in the Canadian prairies. The surface runoff generated during snowmelt is transformed into streamflow or fills numerous depressions driving the focussed recharge of groundwater in this dry setting. The snowpack in the prairies can undergo several cycles of accumulation and depletion in a winter. The timing of the melt affects the mechanisms of snowpack depletion and their hydrological implications. The effects of midwinter melts were investigated at four instrumented sites in the Canadian prairies. Unlike net radiation-driven snowmelt during spring melt, turbulent sensible heat fluxes were the dominant source of energy inputs for midwinter melt occurring in the period with low solar radiation inputs. Midwinter melt events affect several aspects of hydrological cycle with lower runoff ratios than subsequent spring melt events, due to their role in the timing of the focussed recharge. Remote sensing data have shown that midwinter melt events regularly occur under the present climate throughout the Canadian prairies, indicating applicability of the study findings throughout the region.

Chamber for controlling end-tidal gas tensions over sustained periods in humans

1995 ◽  
Vol 78 (3) ◽  
pp. 1088-1091 ◽  
Author(s):  
L. S. Howard ◽  
R. A. Barson ◽  
B. P. Howse ◽  
T. R. McGill ◽  
M. E. McIntyre ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Feedback Mechanism ◽  
Gas Composition ◽  
Short Term ◽  
Average Value ◽  
Nasal Catheter ◽  
End Tidal

Although techniques for the short-term control of end-tidal gases exist, the lack of a satisfactory technique for longer-term control of the end-tidal gases has limited protracted physiological experiments of this nature. We have constructed a chamber in which subjects can be comfortable for many hours while having their end-tidal gas composition monitored and controlled. The system for controlling the end-tidal gas composition is based on a principle described by Swanson and Bellville (J. Appl. Physiol. 39: 377–385, 1975) in which end-tidal PO2 (PETO2) and PCO2 (PETCO2) are monitored and deviations of the actual PETO2 and PETCO2 (PETCO2) are monitored and deviations of the actual PETO2 and PETCO2 from the desired values are corrected by a feedback mechanism that adjusts the inspired gas composition accordingly. End-tidal and inspired gas tensions are measured via a nasal catheter connected to a mass spectrometer. A computer averages the end-tidal and inspired gas tensions and, at 5-min intervals, adjusts the gas composition inside the chamber. During 8 h of isocapnic hypoxia, the system held the 5-min average value for PETO2 within 2 Torr of the desired value (55 Torr) and the value for PETCO2 within 0.35 Torr of the desired value (the resting value for each subject) in four subjects.

scholarly journals Nemo-Nordic 1.0: A NEMO based ocean model for Baltic & North Seas, research and operational applications

2018 ◽  
Author(s):  
Robinson Hordoir ◽  
Lars Axell ◽  
Anders Höglund ◽  
Christian Dieterich ◽  
Filippa Fransner ◽  
...  
Keyword(s):  
Climate Change ◽  
Ocean Model ◽  
Anthropogenic Pressure ◽  
Short Term ◽  
To Come ◽  
Ocean Forecasting ◽  
The Baltic ◽  
Industrialised Countries ◽  
High Degree

Abstract. We present Nemo-Nordic, a Baltic & North Sea model based on the NEMO ocean engine. Surrounded by highly industrialised countries, the Baltic and North seas, and their assets associated with shipping, fishing and tourism; are vulnerable to anthropogenic pressure and climate change. Ocean models providing reliable forecasts, and enabling climatic studies, are important tools for the shipping infrastructure and to get a better understanding of effects of climate change on the marine ecosystems. Nemo-Nordic is intended to come as a tool for both short term and long term simulations, and to be used for ocean forecasting as well as process and climatic studies. Here, the scientific and technical choices within Nemo-Nordic are introduced, and the reasons behind the design of the model and its domain, and the inclusions of the two seas, are explained. The model's ability to represent barotropic and baroclinic dynamics, as well as the vertical structure of the water column, is presented. Biases are shown and discussed. The short term capabilities of the model are presented, and especially its capabilities to represent sea level on an hourly timescale with a high degree of accuracy. We also show that the model can represent longer time scale, with a focus on the Major Baltic Inflows and the variability of deep water salinity in the Baltic Sea.

scholarly journals Spatial variability of mean daily estimates of actual evaporation from remotely sensed imagery and surface reference data

2019 ◽  
Vol 23 (12) ◽  
pp. 4891-4907 ◽  
Author(s):  
Robert N. Armstrong ◽  
John W. Pomeroy ◽  
Lawrence W. Martz
Keyword(s):  
Remote Sensing ◽  
Spatial Variability ◽  
Land Surface ◽  
Management Practices ◽  
Reference Data ◽  
Meteorological Data ◽  
Net Radiation ◽  
Study Region ◽  
Evaporation Model ◽  
Actual Evaporation

Abstract. Land surface evaporation has considerable spatial variability that is not captured by point-scale estimates calculated from meteorological data alone. Knowing how evaporation varies spatially remains an important issue for improving parameterisations of land surface schemes and hydrological models and various land management practices. Satellite-based and aerial remote sensing has been crucial for capturing moderate- to larger-scale surface variables to indirectly estimate evaporative fluxes. However, more recent advances for field research via unmanned aerial vehicles (UAVs) now allow for the acquisition of more highly detailed surface data. Integrating models that can estimate “actual” evaporation from higher-resolution imagery and surface reference data would be valuable to better examine potential impacts of local variations in evaporation on upscaled estimates. This study introduces a novel approach for computing a normalised ratiometric index from surface variables that can be used to obtain more-realistic distributed estimates of actual evaporation. For demonstration purposes the Granger–Gray evaporation model (Granger and Gray, 1989) was applied at a rolling prairie agricultural site in central Saskatchewan, Canada. Visible and thermal images and meteorological reference data required to parameterise the model were obtained at midday. Ratiometric indexes were computed for the key surface variables albedo and net radiation at midday. This allowed point observations of albedo and mean daily net radiation to be scaled across high-resolution images over a large study region. Albedo and net radiation estimates were within 5 %–10 % of measured values. A daily evaporation estimate for a grassed surface was 0.5 mm (23 %) larger than eddy covariance measurements. Spatial variations in key factors driving evaporation and their impacts on upscaled evaporation estimates are also discussed. The methods applied have two key advantages for estimating evaporation over previous remote-sensing approaches: (1) detailed daily estimates of actual evaporation can be directly obtained using a physically based evaporation model, and (2) analysis of more-detailed and more-reliable evaporation estimates may lead to improved methods for upscaling evaporative fluxes to larger areas.

scholarly journals Spatial variability of particle size fractions of an Oxisol cultivated with conilon coffee

Revista CERES ◽  
2012 ◽  
Vol 59 (6) ◽  
pp. 867-872 ◽  
Author(s):  
Julião Soares de Souza Lima ◽  
Rone Batista de Oliveira ◽  
Samuel de Assis Silva
Keyword(s):  
Particle Size ◽  
Spatial Variability ◽  
Clay Fraction ◽  
Soil Samples ◽  
Landscape Configuration ◽  
Sand Fraction ◽  
Size Fractions ◽  
Particle Size Fractions ◽  
Average Value ◽  
Significant Difference

Information on the spatial distribution of particle size fractions is essential for use planning and management of soils. The aim of this work to was to study the spatial variability of particle size fractions of a Typic Hapludox cultivated with conilon coffee. The soil samples were collected at depths of 0-0.20 and 0.20-0.40 m in the coffee canopy projection, totaling 109 georeferentiated points. At the depth of 0.2-0.4 m the clay fraction showed average value significantly higher, while the sand fraction showed was higher in the depth of 0-0.20 m. The silt showed no significant difference between the two depths. The particle size fractions showed medium and high spatial variability. The levels of total sand and clay have positive and negative correlation, respectively, with the altitude of the sampling points, indicating the influence of landscape configuration.

An endemic cephalopod assemblage from the lower Campanian (Late Cretaceous) Parras Shale, western Coahuila, Mexico

2013 ◽  
Vol 87 (5) ◽  
pp. 881-901 ◽  
Author(s):  
Christina Ifrim ◽  
Wolfgang Stinnesbeck ◽  
José Flores Ventura
Keyword(s):  
New Species ◽  
Late Cretaceous ◽  
Species Level ◽  
Short Term ◽  
Faunal Composition ◽  
Cosmopolitan Species ◽  
Generic Composition ◽  
Three New Species ◽  
High Degree ◽  
Lower Campanian

The cephalopods from Union y Progreso represent the first fossil assemblage described from the Parras Shale in Coahuila, Mexico.Pseudoschloenbachia(Pseudoschloenbachia) aff.P. (P.)mexicana(Renz, 1936),P. (P.)mexicana(Renz, 1936),Baculites haresiReeside, 1927, andMenabites(Delawarella)vanuxemi(Morton, 1830) have a geographically restricted occurrence.Didymocerasjuv. sp.,Menuitesjuv. sp.,Polyptychocerasjuv. sp.,Pseudoxybeloceras(Parasolenoceras)juv. sp., andScaphitessp. ex gr.S. hippocrepis(DeKay, 1828) are represented by juveniles and could not be determined to species level.Desmophyllites diphylloides(Forbes, 1846) is the only long-ranging, cosmopolitan species described from this assemblage. Three new species are described:Eutrephoceras irritilasin. sp.,Hypophylloceras(Neophylloceras)arturoin. sp., andTetragonites silencioensisn. sp. The morphotypeBaculitesn. sp. is also inferred to be distinct. The faunal composition of this assemblage indicates a late early Campanian age. This assemblage shows a high degree of endemism. The causes for this endemism are currently unknown and difficult to assess. Nevertheless, the generic composition of the Union y Progreso ammonite assemblage suggests a short-term early Campanian endemic event.

An ultrasound-guided procedure to administer a label of DNA synthesis into fetal sheep

1999 ◽  
Vol 11 (5) ◽  
pp. 303 ◽  
Author(s):  
Paul L. Greenwood ◽  
Ramona M. Slepetis ◽  
Alan W. Bell ◽  
John W. Hermanson
Keyword(s):  
Bolus Dose ◽  
S Phase ◽  
Fetal Weight ◽  
Ultrasound Guided ◽  
Short Term ◽  
Fetal Sheep ◽  
Novel Technique ◽  
Cellular Events ◽  
High Degree

A novel technique was developed to deliver a bolus dose of a DNA label into the peritoneal cavity of fetal sheep at 85–130 days gestation. Use of markers to identify the site of injection in fetuses from litters up to quadruplets, and immunohistochemistry to detect the DNA label, 5-bromo-2¢-deoxyuridine (BrdU), confirmed the procedure was successful in 85% of cases. Duration of the procedure was (mean SD) 44 16 min, and recovery from anaesthesia was rapid and uneventful in all cases. Fetal weight was estimated with a high degree of accuracy (residual standard deviation (RSD) = 297 g and r 2 = 0.93, P<0.001) and the dose of label administered (110 33 mg BrdU/kg fetal weight) was adequate in all cases. BrdU detected in fetal nuclei following injection into amniotic fluid highlights the need for positive identification of the injection site in timed, short-term studies, and suggests potential to further develop the technique to investigate cellular events in fetal sheep younger than 85 days of gestation. The results demonstrate that the procedure can be used to determine in vivo whether or not nuclei have entered the S-phase of the cell cycle.

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